1. Field of the Invention
The present invention relates to an image-taking apparatus which improves accuracy of taken images by correcting image blurring caused by vibration.
2. Description of Related Art
In cameras currently used, operations important for image-taking operation such as exposure determination and focusing, etc., are all automated, and it is very rare that even a person who is not skilled in the camera operations fails image-taking. Recently, a system that represses vibration applied to the camera has also been studied and factors that cause a photographer to fail image-taking have almost been eliminated.
Herein, a vibration control system that represses image blurring (image deflection on an image surface) is briefly described. Vibration of a camera when taking an image is normally vibration with a frequency of 1 Hz through 10 Hz, and as a basic idea that makes it possible to take an image without image blurring even when such vibration occurs during exposure, when an optical vibration control system is taken as an example, it is required that vibration of a camera due to hand vibration is detected and according to the results of this detection a correcting optical unit (comprising a correcting lens and a supporting frame, etc.) is displaced within an optical axis orthogonal plane. Namely, in order to take an image without image blurring even when the camera vibrates, first, the camera vibration must be accurately detected, and second, the optical axis change due to the vibration must be corrected.
In principle, image blurring can be corrected by mounting a vibration detection unit which detects the acceleration, the angular acceleration, the angular velocity, and the angular displacement, by using an accelerometer, vibration gyro, or laser gyro, and carries out proper calculation with respect to the results of this detection, for the camera. Image blurring is corrected by driving a correcting optical unit that makes the image-taking optical axis eccentric depending on the camera vibration detection data supplied from the vibration detection unit.
As the vibration control system, in addition to the above-described optical vibration control system, an electronic vibration control system (electronic correcting system) has also been proposed which repeats image-taking operation a plurality of times with an exposure period the length of which does not cause image blurring, and synthesizes images taken by the plurality of times of image-taking operations while correcting deviations of the images to obtain a taken image (synthesized image) with a long exposure period. This technique has been disclosed in Japanese Patent Application Laid-Open No. H9(1997)-261526.
Recent digital cameras have become smaller than silver-halide compact cameras, and have been so reduced in size that they can be built in a portable electronic apparatus (for example, a portable phone). Under these circumstances, in order to install the above-described optical vibration control system in the camera, the correcting optical unit must be made smaller. However, there is a limitation in downsizing the correcting optical unit since it must support a correcting lens and drive the correcting lens with high accuracy in a large stroke according to vibration.
On the other hand, in the electronic vibration control system disclosed in Japanese Patent Application Laid-Open No. H9 (1997)-261526, the exclusive correcting lens, etc., used in the above-described optical vibration control system becomes unnecessary, so that the entire product can be downsized. Furthermore, the method in which the exposure period for one time image-taking operation is shortened and images obtained through a plurality of times of image-taking operations are synthesized has an advantage in that the vibration control accuracy increases as the exposure period for one time image-taking operation becomes shorter. However, as the exposure period for one time image-taking operation becomes shorter, underexposure increases and image data accuracy lowers, so that it is not possible to obtain an excellent image. In addition, in this method, deviations among the images are detected from characteristic point changes on the images and are corrected, however, in a case where the image exposure is not sufficient at all, characteristic points on the images cannot be reliably identified, and accuracy of correction of deviations among the images lowers and it becomes impossible to synthesize an excellent image. Namely, in the electronic vibration control system, a great vibration control effect cannot be expected.